The present invention relates to an optical thin film processor for the elaboration of unidimensional signals.
As is well known, considerable development has been taking place in recent years in the field of integrated optics. In this field, the main object of research, based on the possibility of obtaining the guided propagation of optical signals in very thin films, is the construction of miniaturized optical systems either with better performance with respect to optical and opto-electronic systems already in use, or with completely new functions.
With respect to traditional optical and opto-electronic systems, the integrated optical systems have the following advantages: smaller size and weight; a smaller feeding power; a greater band width; and a high reliability.
Particular interest has been devoted to the possibility of producing optical analogic processors, in integrated optics, which, in addition to the above-mentioned advantages, are likely to offer the security of a perfect alignment of components, and indifference to mechanical stresses. Such integrated processors may only operate with unidimensional signals, and may therefore be utilized in the field of radar signals and communications.
The signals to be processed are generally time-functions. They must, therefore, be converted into space-modulated light-signals. Their processing takes place by means of a filtering of the spatial frequencies.
Such processing devices include three elements, each of them performing a given function: a guiding system, which allows the guided propagation of the considered signals; an optical system including two or more lenses, to carry out the Fourier's transform of the optical signal; one or more signal modulation and detecting devices, to perform the conversion of the time-signal into a light-signal and vice versa and/or to carry out the filtering of the space-frequencies of the signal.
The basic components proposed for the known devices are currently being improved, and the difficulty met in producing thin-film lenses of a high quality represents a special problem.
Some methods, proposed to produce lenses for integrated optical circuits with plane substrate, are based on the variation of the effective refraction index of the thin layer acting as a wave guide. However, the lenses obtained by following this principle present some serious drawbacks, such as: significant spherical aberration, a reduced optical power, i.e. long focal distances, conversion effect of the propagation modes when passing through the edges of the lenses.
Moreover, their practical construction is complicated because of the need to adopt convenient masks, to deposit the material forming the lens, and of the high precision required.
The aim of the present invention is to produce a thin layer device for the processing of unidimensional signals, likely to eliminate the above-mentioned drawbacks, and to offer very favorable operational characteristics and simple construction.
Such an aim is attained, according to the invention, with an optical thin film device for the processing of unidimensional signals comprising:
(1) A thin film of dielectric material, transparent to the laser radiation, shaped as a spherical lune with an angle of 270.degree., supported by a spherical substrate, made of material with a refraction index lower than that of the thin film.
(2) A point source located on either meridian delimiting the thin film.
(3) Detecting means, located on the other meridian delimiting the thin film.
(4) A modulator located on the meridian laying at 90.degree., with respect to the input meridian.
(5) A device located on the meridian laying at 180.degree. with respect to the input meridian, for the spatial filtering of the signal coming from the modulator located on the meridian laying at 90.degree..
Other features and advantages of the invention will become apparent during the course of the following description.